The HIV Cost and Service Utilization Study (HCSUS) is a unique and extensive data set that allows the testing of important hypotheses among previously under-studied and disadvantaged groups including injection drug users, minorities, and women. Prior work using the HCSUS has not addressed the role of pain in health outcomes and health care utilization. This study proposes a secondary data analysis of the HCSUS to test the associations among pain, health outcomes, use of health services, and illicit drug use in HIV-infected injection drug users (IDUs), non-IDU drug dependent patents, and control patients (non-IDU, non-drug dependent). Understanding the impact of pain on these health-related outcomes and behaviors will inform policy decisions regarding the identification and treatment of pain in these vulnerable individuals. The proposed analyses will: (1) examine how pain impacts HIV-related morbidity, mortality, and use of health services; (2) investigate quality of care for pain by focusing on the possible under-treatment of pain in patients with current or past drug abuse; and (3) examine the extent to which under-treatment of pain contributes to illicit drug use. The proposed research agenda encompasses a set of analyses that will provide valuable insights into the health and well being of IDUs and drug dependent patients in care for HIV.